The electrochemical test strips are widely employed in medical or biochemical test. The known electrochemical test strip has two electrodes for measuring the electrical characteristics of a sample after the sample being injected into a reaction region of the electrochemical test strip. However, in such structure, the electrochemical test strip cannot determine if the sample already covers two electrodes, and even cannot determine if the sample is injected into the reaction region.
To solve the above-mentioned problem, U.S. Pat. No. 5,582,697 disclosed an electrochemical test strip with three electrodes. U.S. Pat. No. 5,582,697 added a third electrode in the reaction region, and the third electrode is disposed farther from an entry of the reaction region than the other two electrodes. After injecting sample, the current variation between the electrode nearest to the entry and the electrode farthest from the entry is detected to determine if the sample appropriately covers the electrodes. To detect the sample, the test strip has to be inserted into an instrument and then electrically connected with the instrument. However, the method disclosed in U.S. Pat. No. 5,582,697 is unable to determine if the test strip is inserted into the instrument correctly, and is unable to determine if the sample is injected into the reaction region until the sample covers most part of the reaction region. In addition, these conventional methods were entirely based on the DC current alone, without considering the influence of AC electrical properties of the sample.
Accordingly, it is advantageous to have an electrochemical test strip capable of determining if it is inserted into a correct position of the instrument, testing the injection condition of the sample, and improving the measurement accuracy.